1. Field of the Invention
This invention relates to a method for steering a robotic lawnmower, leaf-clearing or fertilizing apparatus.
2. Discussion of the Prior Art
Various robotic lawnmowers have been proposed which cut grass or other vegetation without requiring an operator to steer the mower while riding on or walking behind it. Some devices of this nature have relied solely on pre-programmed steering paths for guidance. U.S. Pat. No. 3,650,097 to Nokes illustrates an automatic lawnmower having a path that is pre-programmed on a plastic tape. U.S. Pat. No. 3,789,939 to Geislinger illustrates a programmable cart or lawnmower whose path is programmed on magnetic audio recording tape. Systems such as these are unsatisfactory because of their inability to correct steering errors due to wheel slippage, rough terrain or other obstacles.
Other robotic lawnmowers of the prior art, such as those disclosed by Bellinger in U.S. Pat. Nos. 3,550,714 and 3,570,227, avoid steering correction problems altogether by allowing the mower to move randomly within a boundary defined by a buried cable. When the lawnmower senses the buried cable, it steers away from the boundary toward the center of the bounded area. These systems are disadvantageous because they require a long time to complete the cutting operation. In addition, the task of burying a cable around the entire mowing area is time-consuming and expensive.
The most recent robotic lawnmowers typically utilize some means for self-tracking the cut-uncut grass border. U.S. Pat. Nos. 3,425,197 and 3,924,389, both to Kita, disclose robotic lawnmowers that track a cut-uncut grass border with sensors that are mounted on the front of the mowers. A minute electric signal is produced by each sensor assembly when it contacts the uncut grass. The signal is passed to an amplifier which then acivates a pair of clutch brake mechanisms for steering the mower along the edge of the border.
Other robotic lawnmowers use optical sensors to track the cut-uncut grass border. In U.S. Pat. No. 4,133,404 to Griffin, light is directed toward the border, and a plurality of sensors measures the intensity of the light after it has been reflected from the grass. The position of the cut-uncut grass border is determined by measuring a different reflected light intensity for the cut grass than for the uncut grass. However, if the light-intensity differential between cut and uncut grass is not severe, the system has a low probability of success. A second embodiment disclosed by Griffin employs metal "feelers" which contact the grass. To sense grass, these feelers must be light and sensitive, and their construction may accordingly cause sticking, clogging or breakage. Both types of sensors disclosed by Griffin rely on a complicated comparator method to determine the location of the grass border.
U.S. Pat. Nos. 4,545,453 and 4,573,547, issued to Yoshimura et al, describe automatic vehicles which also track the cut-uncut grass border with optical sensors. These vehicles, however, employ geomagnetic orientation sensors for the intended purpose of remedying the problem of vehicle zig-zagging due to irregularities in the border. The geomagnetic orientation sensors are used with the optical sensors to smooth out the steering of the vehicle.
While the inventors of the above mowing devices have made meritorious attempts to develop robotic machines that satisfactorily perform lawn-cutting operations, the prior art methods have for various reasons failed to satisfy all of the objectives required of such machines.
It is accordingly an objective of the present invention to provide a robotic device capable of efficiently cutting grass, clearing leaves or spreading fertilizer without the assistance of an operator.
It is a further objective of the present invention to provide an improved guidance and control system for a robotic lawnmower that is capable of smoothly tracking a cut-uncut grass border of a lawn with sensors.
A further objective of the invention is to provide a row of sensors that is adapted to detect the location of a cut-uncut grass border relative to the row regardless at which point the border and row of sensors intersect.
A further objective of the invention is to provide a guidance system that utilizes both pre-programmed path information and tracking sensors to guide the robot.
A further objective of the invention is to provide an improved apparatus for programming movement of a robotic lawnmower wherein the programming is accomplished by remotely controlling the movement of the robot over the desired path.
A further objective of the invention is to provide an improved flexibility in programming by allowing the programmed path to be altered by simply redirecting the robotic lawnmower remotely over the desired path.
A further objective of the invention is to provide an improved guidance system that utilizes a computerized digital method to steer the lawnmower straight and smoothly when the grass border is irregular or poorly defined.
A further objective of the invention is to provide a guidance system that can effectively operate even if one or more sensors are defective or blocked by grass, dirt or other debris.
A further objective of the invention is to provide a guidance system that utilizes a computer or other central processor that is capable of taking different courses of action in response to multiple input sensor data.
A further objective of the invention is to provide cutting blades that are safe and energy efficient.
A further objective of the invention is to provide a robotic lawnmower that has increased simplicity and reliability by utilizing very few moving mechanical parts and by utilizing a consolidated drive and steering mechanism that obviates the need for separate mechanisms.
A further objective of the invention is to provide a robotic lawnmower that is efficiently powered by battery.
A further objective of the invention is to provide interchangeable memory modules for the guidance system to enhance flexibility of operation.
Further objectives and advantages of the present invention will be apparent from the following detailed description and accompanying figures.